JPH09209044A - Operation of continuous type steel cast slab heating furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate the temp. of a cast slab and to execute the smooth operation of a cast slab heating furnace by estimating the present steel cast slab temp. from the actual measured atmospheric temp. in each furnace zone and the steel cast slab condition and suitably controlling the atmospheric temp. of each furnace zone. SOLUTION: The present steel cast temp. is estimated by using a distributing constant system temp. model from the actual measured atmospheric temp. in each furnace zone and a position, thickness, width, length, material and charging time of the steel cast slab in each furnace zone in a continuous type steel cast slab heating furnace in a prescribed period. Successively, heating time in each furnace zone is calculated based on the ejecting order of the steel cast slab from the furnace and further, the steel cast slab temp. till ejecting is calculated by the distributing constant system temp. model. From this result, a constant of a concentrating constant system tap. model is decided in each zone in on-line. Further, a target temp. raising pattern, in which the unit requirement of the fuel is minimized, is calculated by using a prescribed evaluating function at the atmospheric tap. obtd. from the concentrating constant system temp. model substituting the decided constant. The atmospheric temp. in each furnace zone is set so as to be heated along this target temp. raising pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a continuous heating furnace for steel slabs, and in particular, it is extracted from the heating furnace by appropriately controlling the atmospheric temperature in the heating zone and the soaking zone. The present invention relates to a technique for setting the temperature of a steel slab (hereinafter referred to as a slab) to a desired value.

[0002]

2. Description of the Related Art In a hot rolling plant of an iron mill, a slab as a raw material for rolling obtained in a preceding step, for example, a continuous casting step is often reheated to a temperature suitable for hot rolling. And
Today, a so-called continuous heating furnace (hereinafter, simply referred to as a heating furnace) having a plurality of furnace chambers (furnace zones) called a pre-tropical zone, a heating zone 2 and a soaking zone 3 is generally used as the heating means.

By the way, as shown in FIG. 1, this heating furnace is long along the production line, and the cast slab 1 is charged.
Not only are the steel types, sizes, and temperatures at the time of charging different, but the heating purpose in each furnace zone 2, 3 is also different, so there are many items to be controlled, and the atmospheric temperature in the furnace (hereinafter referred to as furnace temperature) control, Eventually, combustion control of fuel is very difficult. Therefore, many studies have been made on this furnace temperature control method, a mathematical model for simulating the heating condition of the slab 1 was created based on various measured values, and the model was controlled by operating the computer online. Various methods have been developed.

However, the important items for controlling the furnace temperature of the heating furnace are basically (A) the portion for estimating the temperature at the present position of the slab, and (B) the slab for the heating furnace. A part for obtaining a heating time from charging to extraction, (C) a part for determining an ideal target temperature rising pattern until the target extraction temperature is reached, and (D) a target temperature rising pattern for which the temperature of the slab is determined. It consists of a part that determines the set furnace temperature as close as possible, and of these, particularly regarding (C) and (D), remarkable proposals have been made in recent years.

For example, Japanese Patent Application Laid-Open No. 61-199016 discloses, "When determining a target temperature rising pattern of a slab with a mathematical model, the slab is changed when the fuel flow rate is changed from a current value by a certain constant value. Extraction average temperature, soaking degree, and calculating each furnace zone temperature when the slab passes, to obtain the linear coefficient in the vicinity of the current fuel flow rate value, further extraction average temperature of the slab,
The optimum fuel flow rate that minimizes the fuel flow rate under the condition of soaking degree is obtained using linear programming, and the set furnace temperature of each slab is calculated as a weighted average value from this fuel flow rate and set in each furnace zone. Determine the furnace temperature. The method of controlling the continuous heating furnace is disclosed.

Further, Japanese Patent Laid-Open No. 2-156017 discloses that
“The temperature of each slab is simulated while the fuel flow rate set value in each furnace zone is calculated every moment until the slab is extracted from the heating furnace, and it is set according to the operation purpose such as quality assurance and energy saving. The value of the predetermined evaluation function was obtained, and the target temperature rise pattern of the cast was calculated using a non-linear optimization method such as the steepest descent method so that this value was minimized, and the fuel flow rate and the cast temperature were linearly approximated. Using the model, the fuel flow rate is set so as to approach the target heating pattern obtained above. "

However, JP-A-61-199016
Japanese Patent Laid-Open Publication No. 2-156017 and Japanese Patent Laid-Open Publication No. 2-156017 have final differences that are different from the furnace temperature and the fuel flow rate. Basically, the fuel flow rate and the slab temperature or the fuel flow rate are set. It is the same in that the relationship with the furnace temperature is obtained by linear approximation using a mathematical model. And since these relationships are actually more complicated than the model and are essentially non-linear, the larger the amount of change in fuel flow rate, etc., the greater the error between the actual and calculated results, and There was a problem that the combustion control of the furnace was not performed smoothly.

On the other hand, there is also a method of controlling the combustion of a heating furnace by using a non-linear mathematical model, but this method is very complicated in the optimization calculation of the fuel flow rate and the furnace temperature, and the operation schedule is changed every time. Since the optimization calculation is redone or the optimization calculation itself takes time, there is a problem that the action amount changing action is delayed, and the effect of the optimized calculation is reduced.

In view of this, Japanese Patent Laid-Open No. 3-140415 discloses, "For the purpose of reducing the computer load on-line, the slab temperature is set as a temperature model of a lumped constant system as shown below, and is equal to the temperature at the time of extraction from the furnace. A target temperature rising pattern is determined so that the heat value (the temperature difference of the slab in the part with and without skids for conveying the slab) matches the target value. " Was disclosed.

Θ ₀ = θg− (θg−θi) · exp (−α · t / D) (1 ′) α = a · σ / (ρ · Cp) · (θg ² + θ ₀ ² ) · ( θg + θ ₀ ) (2 ′) where a: correction coefficient [−] Since this method simplifies the temperature model,
The calculation load can be expected to be reduced when obtaining the target heating pattern of the slab or the set furnace temperature.

[0011]

However, in this method as well, since the parameters such as the correction coefficient a and the specific heat Cp are set to constant values (representative values) determined based on the operation results off-line, casting to a heating furnace is performed. As the heating pattern of the material in the heating furnace becomes complicated due to the widening of the charging temperature of the pieces and the variety of steel types, the error in the calculation of the temperature model becomes large. Furthermore, in order to reduce this variation, many stratifications must be performed and parameters must be calculated, which makes management difficult. Further, α in the above formula (2 ′) is an amount indicating how close the slab temperature approaches the furnace temperature θg, and θ ₀ in the above formula (2 ′) is the initial slab temperature θi to t. Slab temperature after time θ ₀
Although it is more reliable as a temperature model to use the time average temperature of the above, there is a drawback that the slab temperature after t hours is simply adopted in the formula (2 ′).

In view of the above circumstances, the present invention has reviewed the lumped constant temperature model used to obtain the target temperature rise pattern of the ingot in the furnace, estimates the ingot temperature with high accuracy, and smoothes the ingot. The aim is to provide a method of achieving the operation of a heating furnace.

[0013]

[Means for Solving the Problems] The inventor has conducted diligent research in order to achieve the above object, devised a method for determining unknown parameters of a lumped constant temperature model, and focused on the combined use of a known distributed constant temperature model. Then, the present invention has been completed. That is, the present invention estimates the temperature of the steel slab while passing through the furnace, and determines the target temperature rise pattern of the steel slab from the estimated value, the target temperature at the time of extraction, and the heating time. In a method for operating a continuous steel slab heating furnace, which sets a heating zone and an atmospheric temperature of a soaking zone so that a piece follows the target temperature rising pattern,
Current steel slab temperature using a distributed constant temperature model based on the measured atmospheric temperature of each smelting zone and the position, thickness, width, length, material, and charging temperature of the steel slab in each furnace zone in a predetermined cycle. And then
Calculate the heating time in each furnace zone based on the extraction order of steel slabs from the furnace, then calculate the steel slab temperature until extraction with the distributed constant system temperature model, and from the results the following lumped constants The constant of the system temperature model is determined online for each zone, and the target temperature rise that minimizes the fuel consumption rate by using the following evaluation function at the ambient temperature obtained from the lumped constant system temperature model in which the constant is substituted It is a method of operating a continuous steel cast slab heating furnace, characterized in that a pattern is calculated and an atmospheric temperature of each furnace zone is set so that the furnace zone is heated according to the target temperature rising pattern.

Θ ₀ = θg− (θg−θi) · exp (−α · t / D) (1) α = 2 · Φcg · σ / (ρ · Cp) · (θg ² + θm ² ) · ( [theta] g + [theta] m) (2) Min (wh * [theta] gh + ws * [theta] gs) (3) Here, since the respective symbols are the same as those described above, they are omitted.

Further, the present invention is characterized in that the calculation of the target temperature rising pattern is performed separately when the position of the steel slab is on the skid and between the skids, and is individually performed. Is also the operating method. According to the present invention, the parameters of the lumped constant system temperature model are determined online based on the temperature calculation results of the distributed constant system (difference model), so it is possible to determine the parameters for each slab and the lumped constant system The accuracy of the temperature model is almost the same as that of the temperature model of the distributed constant system (difference model), and the load on the computer can be reduced. In addition, the obtained temperature model can express a non-linear relationship between the furnace temperature and the slab temperature.The temperature model is used to determine the target temperature rise pattern and to determine the set furnace temperature. A good temperature rise pattern and required furnace temperature can be obtained, and the final operation of the heating furnace will be smooth.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing the outline of the present invention. According to it, the calculation software, which is an important constituent requirement of the present invention, is a "heating time prediction unit" for predicting the heating time in each furnace zone of the slab, a known distribution constant from the furnace temperature actual measurement value of each furnace zone. A "slab temperature estimation unit" that predicts the current temperature of the slab using the system temperature model, a "temperature model determination unit" that determines the constants of the lumped constant system temperature model from these calculation results, and a temperature model determined there Used,
It is formed by the "target temperature rise pattern determination unit" that determines the optimum temperature rise pattern of the slab and the "set furnace temperature determination unit" that calculates the target temperature value of the slab extracted from each furnace zone based on the target temperature rise pattern. ing.

In this case, as a known distributed constant system temperature model, a general partial differential equation of heat transfer (see, for example, Japanese Patent Laid-Open No. 3-140415) is used. Formulas (1) and (2) are used. However, in the present invention, considering the influence of the skid used when the slab moves in the heating furnace, the achievement of the target slab average temperature during extraction from each furnace zone and the skid mark temperature during extraction (material (1) and (2) to keep the difference between the average temperature between skids and the average temperature of the material skids within a certain range.
The formula is calculated separately for the case where the slab is on the skid and the case where it is between the skids. That is,
In the "cast slab temperature estimation unit", the temperatures of the skid portion and the portion including the skid portion as shown in FIG. 2 are calculated using a known two-dimensional difference model. Further, the target slab passes through the heating zone and the soaking zone, and the heating time of each zone is determined by the "heating time prediction unit" from the furnace zone length and the slab moving speed.

Next, the calculation procedure in the present invention will be described. First, the present temperature of the slab obtained by the "slab temperature estimation unit" and the heating time of each band predicted by the "heating time prediction unit" are loaded into the online computer. Then, based on the acquired data, the slab temperature at the time of extraction when heating is performed assuming a certain suitable furnace temperature θg (for example, the current furnace temperature),
The calculation is performed using the same difference model as that used in the above “slab temperature estimation unit”. An example of the result is shown in FIG. Also,
Calculate the average temperature in the skid part for the current temperature, the temperature at the heating zone outlet, and the temperature at the time of soaking in the tropical zone, and set the constants of the lumped constant system temperature model for the average temperature of the skid portion in the heating zone and the soaking zone as follows. decide. When determining the lumped constant temperature model of the heating zone, θi is the current temperature of the slab, θ ₀ is the temperature at the outlet of the heating zone, and when determining the temperature model in the soaking zone, Let θi be the temperature at the outlet of the heating zone, and θ _{0 be} the temperature at the extraction of the soaking zone (see FIG. 4). The constant determining method (a) overall heat absorption rate Φcg is represented by averaging Φcg used for the boundary condition of the difference model.

(B) The average specific heat Cp is calculated from the average temperature of the skid portion at the inlet and outlet of each furnace zone by calculation using the following heat content. Cp = [H (θ ₀ ) −H (θi)] / [θ ₀ −θi] (4) θ ₀ : Average skid temperature at each zone outlet [K °] θi: At each zone inlet Skid part average temperature [K °] H (θ ₀ ): Heat content at temperature θ ₀ [kcal / kg] H (θi): Heat content at temperature θi [kcal / kg] (c) The average temperature θm is calculated by using the equations (1) and (2), the skid average temperature θi at the furnace zone inlet, the skid average temperature θ ₀ at the furnace zone outlet, the heating time t, the furnace temperature θg, and the total heat absorption. Rate Φcg, average specific heat Cp, slab thickness D
Can be uniquely obtained as a solution of the cubic equation.

In this way, the heating zone for the slab in the skid portion and the lumped constant temperature model for soaking are determined. On the other hand, similar to the above, a lumped parameter temperature model of the heating zone and the soaking zone is created for the slabs between the skids. In addition, in the actual calculation, equations (8) to (11) described at the end of this section are used instead of equations (1) and (2).

Further, the target temperature rise pattern of each slab is obtained by using the lumped constant system temperature model determined above, heating constraint condition (a) that the skid part average temperature at the time of furnace extraction is not less than the target temperature, θsS ≧ θmok …… (5) (b) The difference between the skid average temperature and the skid average temperature at the time of furnace extraction is less than the target value, θsM−θsS ≦ θski …… (6) (c) For each furnace zone The furnace temperature must not exceed the upper limit of the equipment, θgh ≦ θghMAX, θgs ≦ θgsMAX (7), and each zone furnace temperature is the minimum among the possible combinations of heating zone furnace temperature and soaking zone temperature. Such an evaluation function (formula (3) above)
And calculate as the only solution. Then, the average temperature of the skid slab at the heating zone outlet when heating is performed with this optimum combination of furnace temperatures is determined as the target temperature at the furnace zone outlet.

Finally, a method for determining the set furnace temperature will be described. By the above method, a lumped constant temperature model corresponding to the current position of a cast piece in the furnace zone is determined. In addition, the "target temperature rise pattern determination unit" defines the target temperature for the skid portion of the slab that leaves the furnace zone at the present time. Therefore, regarding the slab in the heating zone furnace, (8)
For the slab in the soaking zone and the slab in the soaking zone, the equation (9) is used to obtain the furnace temperature for achieving the target temperature at each zone outlet using the Newton method or the like. This furnace temperature is obtained for all the slabs existing in a certain furnace zone, the weighted average of the slabs is performed, and the furnace temperature necessary for the operation is determined. Then, the fuel consumption of the burner provided in each furnace zone is adjusted so as to secure or maintain this set furnace temperature.

FIG. 5 shows an example of heating a slab by adopting the method for operating a continuous steel slab heating furnace according to the present invention. From FIG. 5, it is clear that even if the slab temperature during charging into the heating furnace fluctuates, the slab temperature at the soaking zone outlet has almost reached the target value. Skid unit heating zone temperature model θhS = θgh- (θgh-θiS) · exp (-αhS · th / D) ...... (8) αhS = 2 · ΦcghS · σ / (ρ · CpsS) · (θgs 2 + θmsS 2)・ (Θgs + θmsS) Skid part uniform temperature model θsS = θgs- (θgs-θhS) ・ exp (-αsS ・ ts / D) (9) αsS = 2 ・ ΦcsS ・ σ / (ρ ・ CpsS) ・ (θgs) ² + θmsS ² ) ・ (θgs + θmsS) Skid heating zone temperature model θhM = θgh− (θgh−θiM) · exp (−αhM · th / D) (10) αhM = 2 · ΦcghM · σ / (ρ · CphM ^{) · (θgh 2 + θmhM 2} ) · (θgh + θmhM) skid HazamaHitoshi tropical temperature model θsM = θgs- (θgs-θhM) · exp (-αsM · ts / D) ...... (11) αsM = 2 ΦcgsM · σ / (ρ · CpsM ) · (θgs 2 + θmsM 2) · (θgs + θmsM) where, θgh: heating zone furnace temperature [K °] θgs: soaking furnace temperature [K °] th: heating zone the heating time [ hr] ts: Uniform heating time [hr] θhS: Average temperature of skid part during heating zone [K °] θsS: Average temperature of skid part during uniform zone output [K °] θiS: Initial average temperature of skid part [K °] ΦcghS: Total heat absorption rate of heating zone skid part [-] ΦcgsS: Total heat absorption rate of soaking zone skid [-] CphS: Average specific heat of heating zone skid part [kcal / kg]
K °] CpsS: average specific heat of soaking zone skid part [kcal / kg
K °] θmhS: Average skid temperature in the heating zone furnace [K °] θmsS: Average skid temperature in the soaking zone [K °] θhM: Average temperature between heating zone outlet skids [K °] θsM: Soaking zone Average temperature between outlet skids [K °] ΦcghM: Overall heat absorption rate between heating zones skids [−] ΦcgsM: Overall heat absorption rate between soaking zone skids [−] CphM: Average specific heat between heating zones skids [kcal / kg]
K °] CpsM: Average specific heat between soaking tropical skids [kcal / kg
K °] θmhM: Average temperature between skids in the heating zone furnace [K °] θmsM: Average temperature between skids in the soaking zone [K °] θghMAX: Upper limit temperature of the heating zone furnace [K °] θgsMAX: Soaking zone furnace Upper temperature limit [K °]

[0024]

As described above, according to the present invention, the lumped parameter system temperature model is determined online based on the calculation result of the distributed parameter system (difference model) temperature model. It is possible, and the calculation accuracy of the lumped constant temperature model is almost the same as that of the distributed constant temperature model.
In addition, since the target temperature rise pattern and set furnace temperature are calculated using the obtained lumped parameter system temperature model, the nonlinearity between the furnace temperature and the steel slab can be taken into consideration, and both heating accuracy and computer load can be reduced. As a result, the smooth operation of the heating furnace was achieved.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the present invention.

FIG. 2 is a diagram showing a relationship between a slab and a skid position.

FIG. 3 is a diagram showing changes in a slab temperature calculated by a distributed constant temperature model, a heating element, and a furnace temperature in a soaking zone.

FIG. 4 is a diagram illustrating determination of constants of a lumped constant temperature model.

FIG. 5 is a diagram showing an implementation result of the present invention.

[Explanation of symbols]

 1. Steel slab 2. Heating zone 3. Equal temperature

Claims (2)

[Claims] 1. A steel slab temperature is estimated by estimating the temperature of the steel slab while passing through the furnace, and determining a target temperature rising pattern of the steel slab from the estimated value, the target temperature during extraction, and the heating time. In the operating method of the continuous steel slab heating furnace in which the heating zone and the soaking zone atmosphere temperature are set so as to follow the target heating pattern, the measured atmospheric temperature of each furnace zone and the steel in each furnace zone are set at a predetermined cycle. Estimate the current steel slab temperature using the distributed constant temperature model from the position, thickness, width, length, material and charging temperature of the slab,
Calculate the heating time in each furnace zone based on the extraction order of steel slabs from the furnace, then calculate the steel slab temperature until extraction with the distributed constant system temperature model, and from the results the following lumped constants The constant of the system temperature model is determined online for each zone, and the target temperature rise that minimizes the fuel consumption rate by using the following evaluation function at the ambient temperature obtained from the lumped constant system temperature model in which the constant is substituted A method for operating a continuous steel slab heating furnace, comprising: calculating a pattern and setting an atmospheric temperature of each furnace zone so that the furnace zone is heated according to the target heating pattern. θ ₀ = θg− (θg−θi) · exp (−α · t / D) (1) α = 2 · Φcg · σ / (ρ · Cp) · (θg ² + θm ² ) · (θg + θm) (2) Min (wh × θgh + ws × θgs) (3) Where, θ ₀ : Steel slab temperature [K °] after t hours θi: Initial steel slab temperature [K °] θg: Atmosphere Temperature [K °] t: Heating time [hr] D: Steel slab thickness [m] Φcg: Overall heat absorption rate [−] σ: Stefan Boltzmann constant [kcal / m ² hrK
° ⁴ ] ρ: Specific gravity of steel slab [kg / m ³ ] Cp: Specific heat of steel slab [kcal / kgK °] θm: Average temperature of steel slab [K °] wh: Weight of heating zone atmosphere temperature [- ] Ws: Weight of soaking zone atmosphere temperature [-] θgh: Heating zone atmosphere temperature [K °] θgs: Soaking zone atmosphere temperature [K °] 2. The calculation of the target heating pattern is divided into cases where the position of the steel slab is on the skid and between the skids,
The method for operating a continuous steel slab heating furnace according to claim 1, wherein the method is carried out individually.